This invention relates to a dental implant system which can be inserted into the jaw bone of a patient and can be utilized to improve retention of a dental restoration built onto the jaw bone.
Presently, dental implant systems are utilized to fix a synthetic tooth structure to the jaw bone of a patient in order to replace a missing tooth. The implant system includes an implant which is inserted into a hole in the patient's jaw bone drilled by a dentist. The implant includes a hole designed to receive a dental post which, in turn, serves to retain a core upon which a tooth crown is built. After the implant is inserted into the jaw bone, it is covered by the patient's gum and allowed to heal from 3-6 months while the bone grows to surround and retain the implant. The gum then is opened to expose the implant. At this time, impressions are made or a post needed to support the crown is positioned into the implant. At the present time, these posts are screwed into place with the implant having a helical path and the post having a mating helical thread. The post bottom can have threads or can have a hollow core for a screw to unite the post and implant. A screw system alone does not provide an antirotation characteristic to the implant system and can unscrew and loosen. When multiple implants are placed to support one prosthesis, a tripod effect is created which minimizes lateral and rotational forces onto individual implants. When only two implants are placed or when multiple implants are placed in a straight line to support a single prosthesis, lateral forces created by functional or parafunctional forces stress posts or screws and cause fracture of an implant fixture and/or the post or screw. Single implants incur these forces and rotational forces.
A problem with this system is that the screws break during implacement and during function. Also, the screws are small and may be dropped in the mouth accidently or they are difficult to place into the back portion of the mouth. In addition, it is difficult to determine if a post is fully seated with a screw system. After the post is positioned in the implant, it extends above the gum so that a dental prosthesis including a core can be retained in place. All single posts must resist normal rotational forces which occur during normal or abnormal functions. In general, preformed posts do not provide good stability against rotational force because they are circular and rotate easily when placed in a circular hole in the implant. Screw type posts can exert large lateral stresses which lead to potential implant fixture fracture and implant loss.
It has been proposed in U.S. Pat. Nos. 4,480,997; 4,490,116 and Re 31,948, to utilize a threaded dental post which is introduced into the bore of a tooth stub by being rotated to thread the post into position. The dental post includes a stem portion having a slot extending through the stem thickness and along its length which renders the stem being formed of two legs each having its outside surface threaded. The outside surface of the legs intimately contact the walls of the bore so that the threads on the legs can engage the walls. In addition, a spring-like connection for the two legs is provided so that a radial outward spring force is applied to the legs to force them against the bore walls. These dental posts are undesirable since a rotational force must be applied to the post to position it properly into the bore. This positioning process is undesirable since it is time consuming and causes the patient discomfort. In addition, the possibility exists that the post will be threaded too far which will result in fracture. Furthermore, the radially outward forces of the legs on the tooth stub can result in fracture of the tooth stub over time. The same problems are present when these posts are used in conjunction with an implant positioned in a jaw bone.
U.S. Pat. No. 1,534,409 discloses a two legged post having corrugated surfaces which fit into a root canal having generally parallel walls. This surface design materially reduces the post surface area which contacts the canal walls and thus post retention relies primarily upon cement adhesive strength.
U.S. Pat. No. 5,030,095 discloses an abutment for a dental implant having a collar that ends in a butt joint have a relative flat angle relative to the vertical dimension of the implant. This arrangement is undesirable since debris will remain on the butt joint surfaces when the abutment and implant are joined together to produce a space into which bacteria can infiltrate.
The post forms a tighter fit to the implant at the outside surface of the implant. Implants fail if there is any opening into which bacteria can form infection. Present implants form a junction by squeezing two flat surfaces together forming a butt joint or horizontal interface. Misalignment of the components or debris such as blood or saliva caught on one of the flat surfaces results in an opening at this critical butt joint. In addition, roughness from machining results in opening such that the greater the roughness the greater the resulting openings.
Accordingly, it would be desirable to provide a dental implant having a bore for a dental post which can be inserted into a hole in the jaw. In addition, it would be desirable to provide a dental implant with means to provide mechanical interaction in order to retain the post in the implant hole while minimizing or eliminating fracturing forces on the implant walls exerted by the post. Furthermore it would be desirable to provide a post which resists rotational forces. Furthermore, it would be desirable to provide a system for utilizing such a dental implant and post system which facilitates the placement of a core and a crown. Furthermore, it would be desirable to provide such a system for joining the prosthesis to the post while avoiding a space into which microorganisms can infiltrate. Furthermore it would be desirable to provide a post which maximizes fit on the post to the implant at the joint area while avoiding a space into which microorganisms can infiltrate. Furthermore it would be desirable to provide a post and implant which minimizes post and implant fracture.